Functional Surfaces

The surfaces of tools, semi-finished products and final goods play an essential role in fulfilling technical functions, e.g. with regard to tribology, flow behaviour and coatability.

The research topics embedded in this cross-sectional area are assigned to different research groups and are presented below.

Investigation of Skin-Pass Rolling With a Focus on Surface

An important characteristic of rolled aluminium strips for use in the automotive outer skin is the surface quality. The topography of the surface and in particular the number of roughness peaks as well as the volume of closed lubrication pockets influence the success of the subsequent process steps deep drawing and painting.
The work carried out so far has investigated the relationship between the process kinematics of skin-pass rolling and the transfer mechanisms. For this purpose, the kinematics of a process model of flat rolling was transferred to a mesomodel to describe the surface imprinting. With regard to the imprinting of the surface, a good correspondence between simulation and experiment could be shown.
In the medium term, the numerical model is intended to enable a knowledge-based design of the skin-pass process for aluminium alloys, taking into account global and local influences.

Usually, cold forming processes (e.g. cold forging) are carried out using large quantities of lubricant to reduce friction and wear. The development and realization of a surface layer concept for forming tools, which makes it possible to dispense with lubrication during the cold forging of aluminum, is the central research question of this project. At the Chair of Laser Technology (LLT), the tools are laser structured or laser polished. Subsequently, a quantum-mechanically designed functionalization is applied at the Chair of Materials Chemistry (MCh). The boundary layer concepts are evaluated at the IBF using a self-constructed compression-torsion-tribometer, which can approximate the contact conditions during cold forging.

Specially designed surfaces can reduce the coefficient of friction and shift hydrodynamic lubrication to lower rotational speeds and thus increase the efficiency of bearings. In this regard hemispherical surface structures with a depth and a diameter of 50 µm act as pockets for the lubricant and can store abrasive particles. Additionally, channel-like structures can guide lubricant to the tribological contact zone. The IBF has developed forming operations to manufacture such structures in collaboration with the Chair of Functional Materials, Universität des Saarlandes. The application of these structures on slide and roller bearings showed the beneficial tribological properties successfully.

Riblet rolling is an innovative and newly developed rolling process to manufacture so-called riblet surfaces from ductile metallic materials. A riblet surface consists of small microscopic grooves in the range of 50 µm in rolling direction and is inspired by the skin of sharks. When positioned in flow direction a riblet surface can reduce the frictional drag by approx. 5 %. In addition, a riblet surface has an enlarged surface area, which compared to a normal flat surface, can have certain advantages in terms of thermodynamic or tribological use. The aim of the riblet rolling process is to produce large quantities of durable metallic riblet surfaces in a cost-efficient manner and on a large scale.
To manufacture a riblet surface a work roll is structured using the “MicroWind” process. This creates a negative imprint on the work roll, which is transferred into the rolling stock during rolling. In one single pass the structure is imprinted into the rolling stock.

Other Resources

Institutions

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